According to me, all the techniques should be used. Depending only on directories is not a good practice because if the search engines ban them then all the rankings for the website will go for a toss. Also, getting quality links from authoritative websites will help in increase your website authority as well. Thus, link building should be a combined technique.
One method that you don't have listed and is often forgotten is ON PAGE SEO! I just wrote an article about this, Are you forgetting about on page SEO? On page SEO is optimizing your website pages for the search engines. Back-linking strategies are great and should be where you spend the most of your time, however do not overlook the importance of on-page SEO.
I think the best links are from relevant pages with decent pagerank. In particular, I like on-topic blog posts where I get an anchored link from within the actual body of the post. In my experience, these in-content links are much better than footer or sidebar links. The less out bound links there are on the page, the better it is for you. Link brokers say that relevance doesn't matter much. I disagree, strongly. I also think that having unique content on each page that hosts your link is important. Gone are the days when you could submit one article to 20 directories and actually get 20 real-value links! I'm getting much better results from using unique content (not spun), building links slowly and steadily - and using all original, quality content for my back links. Even my bookmark descriptions are of good quality and are as lengthy as possible.
I like bow one user said it, diversify. Definitely vary your backlinks, don't really on a single strategy. Make sure to have good on-pages as well. Poor on page can significantly impact your rankings
First of all, On-Page SEO is very important, once you are done with that, try to get diversified links.
You can not always depend on the links from the unique medium, you have try to build/get variety links from different medium. Such as Links in Content and industry related Classified Advertising Advertising in a Blog Post Format Social Media and Web 2.0 Concepts Business Classifieds Directory Listing a Business Web Site Ad Network and Link Exchange Text Ad Network
Best SEO Technique are.. 1. Uniq content and on page optimization 2. Proper Site Navigation (them base importance of that page URL structure) 3. Configure your site in such a way to optimize daily activity in your site, like create forum page, blog page etc.. in your site 4. In off page, build up a quality back links.
this is really confusing now, forum posting is worthy or not ? if i have 100 posts at DP then how worty it is??
Blog Commenting and forum posting include signature in a do follow website is best seo technique to get back links and improve ranking on target keywords.
I think both 1. Social Network 2. Forum Posting 3. Article Submission 4. Backlink ( Comment posting on blogs) are very impotent in off page. but never forget Content of our website.
My experiences, for a low competitive keywords, I only do social bookmark and it get to top 10 after some day.